Silicon-on-insulator (SOI) technology offers particular advantages in the fabrication of certain integrated circuit (IC) devices, as well as in other applications. Among these advantages is higher performance over conventional devices, reduced power consumption, improved radiation immunity, smaller die size, and process simplification. Tools that facilitate the economical production of high quality starting material, or wafers, to the SOI community can help drive the technology to greater acceptance.
Several different techniques presently exist to form SOI type wafers. One conventional process employs the implantation of hydrogen into the wafer to assist in fracturing a wafer assembly comprising a wafer with a surface-deposited oxide layer bonded to another silicon wafer. The implanted hydrogen preferentially allows the assembly to fracture along a plane parallel to the oxide surface, resulting in a thin surface silicon-on-oxide sandwich on a silicon substrate.
Another conventional technique employed to form SOI wafers is a technique called “separation by implanted oxygen” (SIMOX). In the SIMOX process, a thin layer (e.g., about 1,000-3,000 Angstroms) of a monocrystalline substrate is separated from the bulk of the substrate by implanting oxygen ions into the wafer to form a buried dielectric layer (BOX). Such implantation conventionally is performed with an implantation dose of about 2×1017 to about 2×1018 oxygen ions/cm2, and the resultant buried dielectric layer ranged in thickness from about 1,000-5,000 Angstroms. The SIMOX process thus results in a heterostructure in which a buried silicon dioxide layer serves as an effective insulator for surface layer electronic devices.
Traditional SIMOX processing employs an ion implantation system, wherein a pencil-shaped beam or a ribbon-shaped beam is generated, mass analyzed and directed toward an end station. The end station is a batch-type end station, wherein a plurality of workpieces or wafers reside and spin about an axis. In pencil-type beams 10, wherein the beam width is substantially smaller than the size of the wafer 12, a magnetic scanner apparatus is employed to radially scan the beam with respect to the endstation, such that as the wafers spin 14 about the axis, the oxygen ion beam scans 16 across each of the wafers, as illustrated in prior art FIG. 1A. The above solution requires a scanning mechanism and associated controller. In addition, as can be seen in prior art FIG. 1B, however, such a scanning process is not trivial; rather since some portions of the beam will be traversed twice per full scan, while other portions are scanned only once, a moderately sophisticated scan and rotation control architecture must be controlled to emulate a typically desirable Lissajou pattern.
When employing a ribbon-shaped beam 20 as illustrated in FIGS. 2A and 2B, the width 22 of the beam is typically larger than the diameter 24 of the wafer 12, and thus many of the above challenges associated with the above conventional scanning process are avoided. Use of a ribbon-beam 20, however, has challenges with respect to wafer cooling. Typically, a SIMOX process is controlled modestly stringently at about 600C such that the implantation self-anneals to repair the lattice of the wafer. Thus challenges exist to balance the beam power with radiative cooling that is employed as the wafer spins about the axis. In addition, although the ribbon-beam does not have to scan across the wafer, since the wafers are off-axis the current density seen by portions of the wafer further away from the axis decreases by 1/r, wherein r is the distance from the axis to the portion of the wafer at issue. Thus, non-uniform implantation and thermal effects may occur unless additional control is employed. Varying the current density of the ribbon-beam along its width to accommodate for the above variation is rather challenging and requires further system complexities.